1. Field of the Invention
The present invention provides a system for determining the flow rate of a fluid. The invention may be used for measuring the rate of fluid flow and may be included in a larger system for controlling the flow rate of the fluid. More particularly, the invention provides an improved flow meter which includes a ferrous floating internal piston in a reciprocating flow meter, wherein the internal piston is magnetically tied to a coupling arm with an end in magnetic contact with a linear digital encoding transducer equivalent in operable length to the full stroke of the ferrous floating internal piston and which provides immediate data regarding the smallest movement of the internal piston.
2. Description of the Related Art
Systems for measuring fluid flow rates and for introducing measured fluids into flowing fluids are well known. Systems for measuring fluid flow rates are desirable in devices or systems where flow rates must be controlled or verified. Measurement of flow which is accurate, highly precise (high resolution), and consistent is important in various systems utilizing fluid flow for operation. Measurement of those flow rates often must be expressed and communicated in an electronic format that is compatible with programmable logic devices. Moreover, it is desirable to have a high turndown in these systems, although typically one of the most substantial problems with existing meters. Existing meters thus have a narrow (often very narrow) range of operations, problematic in cases of fuel injection where flow may operate between zero flow and high flow rates.
Systems for delivering fluids, including those for introducing fluids as additives into other fluid flows, are well known in the art and are generally desired where the fluid may have a limited duration of effectiveness after introduction to a flowing untreated fluid, particularly in cases where additives may be selected on site based on the specific need at the time. In some of these applications, it is necessary to precisely control the flow of the metered fluid, such as an additive, relative to the flow of a second fluid, such as fuel, being delivered so as to maintain a ratio of fuel to additive, usually represented in parts per million. This can be particularly critical where the flow of the second fluid is relatively low, driving down the flow rate of the metered fluid. Thus, doing so requires accurate measurement of the additive, particularly where usually delivered at a very low flow rate.
With regard to addition of a treating agent, the efficacy of the treated fluid may be effected if the proper volume of additive is not introduced to the untreated flow of a process stream at the current flow rate. Additionally, the cost of the additive to be introduced may be quite high, so cost-effectiveness requires the flow rate, as measured by a flow meter and potentially communicated to an associated logic controller which may in turn control the pump supplying the additive. Ensuring consistent delivery of additive to the untreated fluid is a necessity. Introduction of additive at actual flow rates which are above or below the desired flow rate is undesirable, such as in cases where the additive is introduced to an untreated flow of a petroleum-based fluid where combustion may be over- or under-pressurized in the engine, potentially posing a danger to operators and others. Moreover, other additives effect lubricity or conductivity of fuel with each having the need to be injected accurately over a wide (often very wide) range of flow.
Thus, accuracy, high resolution, and consistency are needed for systems utilizing fluid flow, including systems where additives are used in conjunction with motor and aviation fuels, water-treatment systems, and other systems.
Among the prior art devices directed to determining the flow rate of a fluid flow, either for determination of flow rates or for addition of a treating agent are positive displacement meters such as oval gear flow meters, which may consist of two close tolerance oval gears which, when fluid is passed between the two, produce a rotary motion within the meter housing. A shaft connected to one of the meter oval gears includes a rotating hall affect sensor that is used to signal the speed of the rotating shaft. A revolution of the shaft represents a certain volume of fluid passing through the meter by virtue of the volumetric displacement between the two gears inside the meter housing. Meters of this type are very sensitive to solids since the tolerances within the meter are very close. Such meters are prone to clogging and locking up as a result of various foreign material found in fluids such as additives or treating agents. In addition, many fluids, additives or treating agents have solids that are a part of the fluid, additive or treating agent itself which tend to be highly abrasive. This abrasiveness quickly wears the meter and causes it to quickly lose efficiency and its ability to accurately reflect the volume passing through the meter. Additives such as dyes are very abrasive with a high solids content making them inappropriate for use with oval gear meters. Many fuel additives are injected at extremely small ratios as low as 1 PPM. Oval gear meters require minimum flow rates that far exceed those rates found in additive injection, making them inoperable in these applications.
Other prior art metering systems have included float type flow meters that have utilized floats in static, vertically-aligned flows, and reciprocating pistons which have generally measured flow rate according to travel of the reciprocating piston from one end of the associated cylinder to the other.
Such metering systems are of limited utility in measuring flow rates. Float systems similarly are of limited benefit where the system is susceptible to being out of vertical alignment.
Where used for additive delivery in fuels, such metering systems are of limited utility, specifically where the volume of additive introduced is particularly small relative of the untreated fluid (such as less (preferably substantially less) than 0.25% or, non-equivalently less than 2500 parts per million (PPM) (additive to fuel)). Substantially higher ratios approach the concept of blending.
In addition to the foregoing, due to the minute amount of additive dispensed, and the long time needed for the typical reciprocating metering system to complete one cycle (and hence provide a flow rate) that real time flow rates cannot be obtained the resulting flow rate has not assurance that the resulting average is consistent with the dispensing rate throughout the cycle.
There is therefore a need for an accurate meter flow which performs without reference to the system's orientation with minimal moving parts. There is also a need for a flow meter with a high turndown, providing a wide range of operation. There is also a need to control the flow rate of a relatively minute volume of additive to be dispensed into a flow of untreated fluid by providing a high resolution additive delivery system, to monitor the flow rate of a fluid with high resolution, or to maintain at high resolution a desired flow rate of additive.